Corrélations Phénotypiques et génétiques entre critères endocriniens et mesures testiculaires chez les jeunes mâles Romanov et le taux d’ovulation à 8 mois de leurs demi-soeurs

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Corrélations Phénotypiques et génétiques entre critères endocriniens et mesures testiculaires chez les jeunes mâles Romanov et le taux d’ovulation à 8 mois de leurs

demi-soeurs

G. Ricordeau, Julien Pelletier, M. Courot, Jacques Thimonier

To cite this version:

G. Ricordeau, Julien Pelletier, M. Courot, Jacques Thimonier. Corrélations Phénotypiques et géné-

tiques entre critères endocriniens et mesures testiculaires chez les jeunes mâles Romanov et le taux

d’ovulation à 8 mois de leurs demi-soeurs. Genetics Selection Evolution, BioMed Central, 1979, 11

(2), pp.145-159. �hal-02729329�

Phenotypic ^and genetic relationships between endocrine cri- teria and testicular measurements of young ^{Romanov rams} and the ovulation rates at 8 months of their half-sisters

G. RICORDEAU J. ^{PELLETIER, M. COUROT} J. ^THIMONIER

F. EYCHENNE R. MOLLARET R. DUZERT D. LAJOUS A.CARATY

(

*

) Station d’Amélioration Génétique ^des Animaux, Centre de Recherches de Toulouse, ^LN.R.A.

B.P. _{12 ,} 31320 Castanet Tolosan Station de Physiologie ^{de la} Reproduction,

Centre de Recherches de Tours, LN.R.A.. 373 8o Nouzilly

Summary

The object ^{of this} study ^{was to} estimate the relationships between levels of plasma ^L.H

of male I?omanov lambs at ¢,6 ^{and 8} weeks, ^their testicular growth and the ovulation rate of their

paternal half-sisters. Sixty-eight ^{lambs were} involved in 197 6 and !¢ in 1977 from ^a total of 14

sires. At eacli age, 3 samples ^{of blood were} taken and the te,ticular diameter was measured at ¢ 2 , 70 and ¹⁰⁰ days ⁱⁿ 197 6, and at 70 , ¹⁰⁰ and 140 days in 1977 .

The mean level of L.H. was a maximum at 6 weeks of age and the correlation between ^mean L.H. levels at 6 and 8 weeks was highly significant. Differences between progeny of sires for

mean L.H. levels (calculated from the 3 ages together) and testicular growth ^between 70 ^and

ioo days (corrected ^fcr liveweight) ^were only highly significant in 1977 .

All correlations between L.H. levels and testicular measurements were non-significant.

The mean ovulation rates of each sire’s ^ewe lambs were independent ^{of the mean} L.H. level of their half-brothers, although ^{there was a} positive ^but non-significant correlation with the tes- ticular growth from 70 ^{to 100} days of their half-brothers ( 0 . 43 ; ⁿ

14 ).

The high pulse frequency ^{of LH} levels of lambs at this age did net interfere with the results obtained as was shown by ^a complementary study of r¢ lambs from which blood samples ^were.

taken at 20 minute intervals for 6 hours at both 6 and 8 weeks of age.

Introduction

The gonadotropic ^{hormones I,. H. and F.S.H.} ( * ) ^can be measured at birth in the blood plasma of both male and female lambs. The observations of T HI - MONIER

, P ELL ET I E R and LAND (ig 7 2), then those of B LAN C ^el al. ( 1975 ) ^indicated

(

*

) L v teinizing hormone and Follicle-stimulating ^hormone.

that between 4 and ^I weeks, the level and variation of plasma L.H. concentration of lambs depends ^{on the} genetic type and is related ^to ovulation rates among females of the same type. ^{C ARR and LAND} ( 1975 ) ^{observed a} comparable ^result

with _young males from 7 ^to 13 weeks, ^but !cx2!RrrxeMP ^and I,AS2!R ( 197 6),

HA NR A HAN

et al. (1977) ^and WESTHUYSEN and DWRxs! (1977) ^{did not observe}

the correlation. In the same breed, ^Birrnorr ( 1973 ) showed that at 3 o days, male and female lambs from _groups selected for high fertility ^had higher ^levels

of plasma ^{I,.H. than lambs from} groups selected for low fertility. ^{BirrDOrr also} presented evidence of significant differences in plasma ^I,H levels between families and between type of birth classes. T ROUN S ON et al. ( 1974 ) confirmed this result in comparing measurements made at 5 ^months among males from _groups selected for either high ^{or low} fertility. However, ^{BirrDON and PIPER} ( 197 6) ^{noted that}

in their 0, ^{T and B Merino} flocks, ^{there was no} correlation between the concentr- ation of I,H of female lambs at 3 o days of age and subsequent ^litter size, ^irres- pective of whether I,H ^was determined from a single sample ^{or a series. In other} experiments, ^I,a!n (1 97 2, 1973 and 1977 ), ^{LAND and CA R R} (1975) showed that testicular growth ^{was more} rapid ⁱⁿ genetically highly ^fertile types ^{and that} selection of Finn-Dorset sheep ^{for or} against testicular growth caused differences in fertility ^and fecundity ^{of ewes at I} year of _age.

This study ^{aimed to} verify these results within a highly ^fertile breed, by comparing plasma L.H. levels and testicular growth of young Romanov ^rams with the first reproductive performance ^{of their} paternal half-sisters.

Materials and methods

This study ^{was made} using male and female lambs which were the progeny

of 14 ^{Romanov rams} following ^the protocol ^{outlined in table 1 .}

1

.

Measurements

All lambs were weighed ^{at birth} (January-february), ^{then each 3 weeks.}

Age-adjusted weights ^were calculated by ^linear interpolation for standard _ages of 4 0, 70, ¹⁰⁰ and 140 days.

Two sets of measurements were made on the male lambs:

a) ^Blood samples ^{were taken at} 4 , 6 and 8 weeks (± ³ days). ^{At each} age, 3 samples ^{were collected at intervals of 1 hour} starting ^at 8. 3 o ^am. Immediately

after collection, ^the samples ^were stored in ice. They ^were centrifuged ^{and the} plasma ^{drawn of£} approximately ⁱ hour after collection. The plasma samples

were stored at

i2 °C until their I,H concentration was measured by ^{the radio-} immunoassay ^described by ^{P ELLETIER et at.} ( 19 68). The results are given ⁱⁿ ng /ml ^of plasma: ^solution I,H..M 3

^{1 .8 I,H - NIH - S 1 . The} samples ^from

each annual series ( 197 6 ^and 1977 ) ^were measured in ^one assay, but with one

year between collections which could explain the difference in I,.H. level from

one series to the other.

b) Measurement of the diameter of the right ^testicle (including ^{the thick-}

ness of scrotal skin) ^{was made with a set of} callipers ^at q. 2 , 7 o and 100 days ⁱⁿ 197 6

and 70 , ¹⁰⁰ and 140 days in 1977 ( * ).

Average litter sizes ^were 2 . 9 for the 68 lambs born in 197 6 ( 1 6 ^{p. 100 twins,} 6

9 ^{p. 100} triplets ^{and r 3} p. ^ioo quadruplets) and 3 . 2 for the 93 lambs ^born in 1 977

(8 ^{p. 100 twins, 5 4 p. 100} triplets ^{and 34} p. ¹⁰⁰ quadruplets).

Ewe lambs belonging ^{to the same families as} these males were observed at 9

months of age. Their ovulation rates were estimated from the number of ^cor- pora lutea observed using ^an endoscope ^{as described} by ^{T HIMONI E R and M AULPOX} (I969) !

2

.

Statistical analysis

As measures of I,.H. concentrations had an asymetric distribution, ^a square- root transformation was used for analysis. ^{In order to} estimate basal I,.H. level, excluding peaks, ^{an « I,.H.} minimum value was taken to be the lowest of the 3 hourly ^{measures of I,.H. at each} age. Statistical tests, correlations and ^ana-

lysis of variance were calculated only ^{on the} transformed measurements. Repeat- ability ^was calculated from the intraclass correlation (p) ^after analysis ^of variance, and from the mean of correlation coefficients between the observed measurements (r).

In order to eliminate the influence of live weight ^{on measures} of testicular diameter, age-adjusted ^{diameters were corrected} using the linear regression ^of

diameter on weight calculated for each standard _age. This allowed the calcul- ation of corrected testicular diameter (C. TD) and corrected testicular growth (C. TG).

On account of the differences in I,.H. levels and variances in 197 6 and 1977 , correlations and analysis of variance have been calculated separately ^{for each}

year. Mean correlations ^were then calculated after Z transformations of the

separate correlations. In view of the small numbers of _progeny, we have not estimated heritabilities or genetic correlations from the half-sibs progeny groups.

(

*

) Two males in rg 7 6 and another 2 in ig77 which had ^uneven testicles were eliminated from the

study.

Results

1.

Observations ^on young males

1

. LH levels

a) ^{On the} whole, the effect of _age was highly significant. The level of LH

was a maximum at 6 weeks and was significantly ^{different to} that observed at 4

weeks in both 197 6 and 1977 . There were no significant differences between LH levels at 6 and 8 weeks, except ^{for a} difference between mean VLH ^minimum

levels in 1977 (Table 2 a).

2

. Testicular growth

Taking ^the two years together, testicular diameters were: z. 7 , 3 .0, 4 .2 and 5.z cm

at 42 , 70 , ¹⁰⁰ and 140 days respectively (Table ^{2 ,} fig. i). ^The repeatabilities ^of

testicular diameter at 30 ^or 40 day ^{intervals were} relatively ^low ( 0 . 23 ^to 0 .5 4 ),

the best being ⁱⁿ 1977 with the second operator (Table 3 c).

Age corrected testicular diameters were very significantly correlated with

liveweight. Table q. gives ^these correlations and the observed regressions.

3

. Genetic differences

The results of analysis of variance (table 5 a) ^show that between-sire diffe-

rences were significant ^{at 6 weeks in} 197 6 ^{and at both 4} and 8 weeks in 1977 for

mean f i X. ^{However they were only very} significant ^{for mean} VLH ^calculated

on the _{3 ages} together in 1977 . ^The significances ^{of the} sire effects for the variable

1 /

i/H minimum ^{at the 3 ages were similar to those} obtained with the variable

mean !I,H.

With testicular measurements, between-sire differences were just significant

for corrected testicular diameter at 100 days ⁱⁿ 1977 , ^but very significant ^for

corrected testicular growth from 70 - I oo days ^{in the same} year (Table 5b).

On the basis of the results from the 2 years together ( 14 families), ^mean VLH

measured from 4 ^{to 8 weeks} and testicular growth between 70 and ¹⁰⁰ days appear to be heritable characters. In particular, estimates of heritability (h 2 ) ^calculated

from the components of variance of table _{3 a,} are higher than the estimates of B

INDON et CFI’ AN G ( 197 6) who observed an h 2 of less than 0 . 10 on young lambs measured four times at 30 minute intervals.

4

. Correlations between variables (Table 6)

All of the correlations between I,H ^levels (mean )LH ^{at 6, 8 and 4 to 8 weeks)}

and testicular measurements (C.TD ^{at ioo} days; ^{C.TG from} 42 ^{to 100} days ^or

from 70 ^{to 100} days) ^{were small and} non-significant.

Increase in testicular diameter (corrected ^for liveweight) ^{was not associated}

with weight ^at 70 days, but over-all it was significantly correlated to litter size:

- 0.36 ^{for C.TG} 42 - 100 days ⁱⁿ 197 6 ^{and -!-} 0 .24 for C.TG 70- I oo days in 1 977 .

II.

Correlations between half-sib families

Because of the between-year differences in I,.H. levels and the between-

family differences in ovulation rate each _year ( 2 . 12

^{2.30 in} rg76; 2,30

2.89

in i g 77 ), correlations were calculated separately ^for each series and mean corre-

lations estimated from these (Table 7 ). ^{Mean ovulation rates} of half-sibs were

practically independent ^{of mean I,.H.} levels in the ram lambs. However there

was a positive ^but non-significant correlation ( 0 . 43 ) between ovulation rate and

corrected testicular growth from 70 ^{to 1 00} days.

Discussion

I

.

Variability of ^L.H. measurements

The results of this study ^confirm previous observations on the patterns ^of change ^of plasma I,.H. levels (THIMONI!R et ^al., I g 72 ; Br, AN C et al., I g 75 ; ^{CoTTA et} al., Ig75; LAND ^and CARR, Ig75; ^{COUROT et} al., I g75; ^{I,!! et} al., 1976;EcHTERNKAMP

and RASTER, 1976; ^{HANRA H A N et al.,} 1977), although measurement periods ^and sampling ^{methods were not the same. For} example, ^blood samples ^{were taken}

here at hourly intervals, ^{while some} other authors used intervals of 15 , 20 , 30 ^or 90 minutes.

The repeatability ^{of I,.H. measures, between} measurement times at the same

age ^or between mean measurements at the _{3 ages,} differed from one year to the next. This was probably ^a result of the pulse-like release of I,.H. that the sam-

pling ^{was not able to cover with} precision. ^While the correlation between mean

L.H. level ^at 4 and 8 weeks ^{was zero or} only just significant (which corresponds ^{to the}

results of H ANRAHAN et al., I g 77 ; ^{G ABINA and} FoI,CH, I g 7 g), that observed between 6 and 8 weeks was always highly significant. Overall, repeatability ^{was no}

better for the variable )LH ^minimum, which eliminates in part ^{the influence} of discontinuous release of I,H, ^{a result} also observed by ^{W ESTHUYS E N and}

D IER

KSE (1977).

With testicular growth ^{from 6 to 20} weeks, ^the observed diameters for Roma-

nov rams born in January-February ^were very close to those obtained with Finn-

sheep ^{born in} March-April (LAND ^{and SALES,} I g 77 ), although, ^{here also, the mea-}

surement method was slightly ^{different as} scrotal skin thickness, which represents 5 ^to 7 mm, ^was not deducted in this study.

2

.

Relationships between L.H. and testicular measurements

Over the 2 years, the mean L. H. level of Romanov ram lambs was independent

of their type of birth. This result _agrees with the observation of H ANRAHAN et al. ( 1977 ) but differs from those of B INDON (t 973 ) ^{who found a} higher ^{level of}

I,.H. ^at 30 days among Merinos born in multiple ^births compared ^{to those born}

as singles. ^In addition, ^{like G ABINA and} FoI,cH ( I g 7 g; ^Rasa Aragonesa lambs),

we found no significant correlation between I,.H. level and testicular measurements,

although ^a positive ^and significant correlation was reported by ^{C ARR and LAND} (

I97S

; I4 lambs from ₃ breeds), ^{H ANRAHAN and} Q UIRK E ( I g 77 ; pooled correlation of _{o. 3 o} from 6 genetic groups having within-group correlations varying from 0 . 03 to 0 . 72 , C f. HA NR A H AN, 1976).

With more frequent ^blood samplings, ^{it is} possible ^{to trace with} precision ^the

LH secretion profile. ^{Thus, at} the time of interpreting ^these results, ^{it was} considered that the absence of an observed correlation in this study may have been due in part ^{to the} relatively imprecise sampling ^routine. Consequently

a supplementary ^{control was} established in 197 8 with I q. ^{Romanov ram} lambs.

Measurements were made at 6 and 8 weeks and, at each _age, 19 blood samples

were taken at 20 minute intervals from 8 a.m to 2 p.m. Two sets of testicular

measurements were also made: testicular diameter at 100 days and testicular

growth between 70 and ¹⁰⁰ days. ^{From the} groups of measurements at 6 and 8 weeks, four criteria were defined for each ram lamb (table 8):

i) ^Mean of the 19 measurements.

2

) ^{Number of} peaks ^observed during the 6 hours of sampling.

3

) ^{The mean of the} lowest 5 values of ^each series of 19 ^as estimates of the base level of I,.H.

4

) ^{Means of} measurements z, q. and 7 for comparison ^{with the} 3 measurements made in 1976 and 1977 (samples 4 and 7 ^were taken i hour and 2 hours after the first).

Statistical analyses of these data show that the correlation between criteria

i and 4 ^was relatively strong ( 0 .77), that correlations between criteria _{1 ,} 2 and 3 ^on the one hand and the 2 testicular measurements on the other, ^were practic- ally ^zero. The observations are based on small numbers of lambs but they give

no reason to detract from the results of the ² preceeding ^years.

3

.

Correlations between sexes for ^the different Parameters

At the _progeny level, the ovulation rates of _young ewes are practically ^inde- pendent ^of measurements of I,.H. in their half-brothers, although they ^{had a} positive ^but non-significant correlation with testicular growth between 70 and

100 days. ^{This last} criterion is probably ^{a better} reflection of _{the group} of hypo- physeal ^factors controlling ^{the male} gonads, ^{than the} single ^{hormone I,.H., thus} explaining the better correlation. This encouraging result confirms the indirect responses observed in ovulation rate or prolificacy following direct selection for testicular growth, ^{and the reverse: LAND} ( 1977 , 1979 ) and H!rrRAHarr and Q UIRK E (

1972

) ^with sheep; ^{I SL A M et al.} ( 197 6) ^{with mice; P R O UD et al.} (1976) ^and I,>;Geur,T

et al. ( 1979 ) ^with pigs. ^{However it is} necessary to continue this work with larger

numbers of animals of different breeds and litter sizes in order to determine which method (individual ^{selection or} rapid family testing) and with what efficiency,

measurements of testicular growth ^can assist in selection for fertility among sheep.

It is appropriate ^to emphasise ^{that this work was carried out} using ^{a well}

defined character (ovulation ^{rate of ewes at} 9 montns) ^{but with Romanov families}

that showed relatively little variation in this criterion. This could explain why

no relationship ^was observed between male I,H levels and ewe lamb ovulation rates.

Reçu pour publication ^{en octobre} ig 7 g.

Acknowledgements

We thank R. Rouvma for aids to statistical analysis and W. A. P ATTIE for the translation

of the french manuscrit.

Résumé

* Corrélations PhénotYPiques ^et génétiques ^entre critères endocriniens et mesures

testiculaires chez les jeunes ^{mâles Romanov et le taux} d’ovulation à 8 mois de leurs demi-sœurs.

Cette étude a pour but d’estimer les relations entre le niveau de LH plasmatique ^des jeunes

mâles de race Homanov à ¢, 6 et 8 semaines (à chaque âge, 3 prélèvements de sang à ⁱ heure d’in-

tervalle), leur croissance testiculaire de 40 à 140 jours et le taux d’ovulation de leurs demi-soeurs de père. ^{Elle concerne} 68 agneaux ^en 197 6 ^et 74 agneaux ^en 1977 , issus au total de 14 pères.

Le niveau moyen de LH ^est maximum à 6 semaines et la corrélation entre les niveaux moyens de LH à 6 et 8 semaines est très significative. ^Les différences entre pères pour le niveau moyen de LH calculé sur l’ensemble des 3 âges ^et l’accroissement des testicules entre 70 et ¹⁰⁰ jours corrigé pour le poids ^{vif ne sont très} significatives qu’en 1977 .

Toutes les corrélations entre le niveau de LH et les mesures testiculaires sont non signifi-

catives. Le taux d’ovulation moyen des filles est indépendant ^{du niveau} moyen de ^{LH de leurs} demi-frères; ^{il est en} corrélation positive, ^{mais non} significative, ^avec l’accroissement testiculaire de 70 à ¹⁰⁰ jours (+ ^{0 . 43 avec n =} 14).

La pulsatilité élevée de LH chez les agneaux de cet âge n’interfère pas ^sur les résultats obtenus comme le montre une série complémentaire de 14 agneaux ^sur lesquels ^les prélèvements

ont été effectués à 20 minutes d’intervalle pendant 6 heures et à l’âge ^{de 6 et} 8 semaines.

References

B

INDON B. M., 1973 . Genetic differences in plasma luteinizing hormone of the prepubertal

lamb. J . R eprod. Fert., 32, 3 4 7-34 8 .

B INDON

B. M., ^{PIPER L.} R., 197 6. Assessment of new and traditional techniques of selection for reproductive ^{rate. In}

Sheep Breeding ^{». Ed. G.} J. TOMES, D. E. R OBERTSON and R. J.

L IGHTFOOT

. West. Aust. Inst. Tecknol., 357-37I!

B INDON

B. M., ^{C H ’ ANG T.} S., 197 6. Unpublished. ^Cited by ^{B INDON and PIPER,} 197 6.

B INDON

B. M., TURNER H. N., 1974 . Plasma LH of the prepubertal ^{lamb: a} possible early

indicator of fecundity. J. Reprod. ^{Fert., 39,} 8 5 -88.

B

LANC M., ^{CO UR OT} M., ^PELLETIER J., ^{T H IMONIER} J., 1975 . Unpublished. ^Cited by ^{T HIM O NI E R} J.,

I975

: )!tude de la puberte ^{et de} la saison sexuelle chez les races prolifiques ^{et leurs} croisements

avec des races fran!aises. journie de la Recherche ovine et caprine, ^{LN.R.A. et} LT.O.V.T.C., Paris, S.P.E.O.C., II, 1 8- 27 .

C ARR

W. R., ^{LAND R.} B., 1975 . Plasma luteinizing ^hormone levels and testis diameters of ram

lambs of different breeds. J . R eprod. ^{Fert., 42,} 325-333.

C

OTTA Y., T ERQUI M., ^{P ELLETIER} J., ^{C OUROT} M., I975 . Plasma testosterone and LH in lambs from birth to puberty. C. R. Acad. Sci., Paris, D, 280, I4y3-I476!

Couxox M., de R EVIERS M. M., ^{P ELLETI ER} J., 1975 . Variations in pituitary and blood LH

during puberty ⁱⁿ the male lamb. Relation to time of birth. Ann. Biol. Anim. Bioch. Biophys., 15, 509-516.

Ecxxr:RNxAMP S. E., ^{L ASTER D.} B., 197 6. ^{Plasma LH} concentrations for prepubertal, postpu- b

e r ta l

, ^{a n est ro u s and} cyclic ^{ewes of} varying fecundity. J. ^{Anim .} Sci ., 42 , 444-447!

G

ABINA D., ^FoLCH J., 1979 . Vaviabilidad Genetica del Cvecimiento testieular y de ^{la tasa de LH}

en el covdevo de Raza Rasa Avagonesa. Symposium ^on sheep and cattle reproduction. Saragoza,

may 1979.

H

ANRAHAN J. ^P., 197 6. Testis diametev in vam lambs and selection for litter size. In An Foras Taluntais Anim. Prod. Research. Report. p. 1 6 7 (abstr.).

H

ANRAHAN J. P., Q UIRKE J. ^F., 1977 . Testis size and plasma luteinizing ^{hormone as aids to}

selection for fecundity ⁱⁿ sheep. ^Anim. Prod., 24, 14 8 (Abstr.).

H

ANRAHAN J. ^P., QU I R KE J. ^{F., GOSLING} J. ^P., 1977 . Genetic and non-genetic ^{effects on} plasma

LH concentrations in lambs at 4 and 8 weeks of age. J. Reprod. Fert., 51, 343-349.

ISLAM M AFIZUL A. B. M., ^{HILL W.} G., ^{LAND R.} B., I9!6. Ovulation rate of lines of mice selected for testis weight. ^{Genet. Res., 27, 23 - 32 .}

LAND R. B., 1972 . Is mammalian fertility ^{sex limited?} J. Reprod. Fert., 31, 512 .

LAND R. B., 1973 . The expression of female sex-limited characters in the male. Nature, 241, 2

08-209.

LAND R. B., 1977 . Testis measuvement as an aid to genetic ^selection for female reproduction.

Report A.B.R.O., 1977 , 23-29.

LAND R. B., 1979 . Reproductive Physiology ^and genetic ^selection for reproductive ^traits. Sympo-

sium on sheep ^{and cattle} reproduction. Saragoza, may 1979 .

LAND R. B., C ARR W. R., I9!5. Testis growth ^and plasma ^LH concentration following ^hemicas- tration and its relation with female prolificacy ⁱⁿ sheep. J. Reprod. Fert., 45, 495 - 5°1 . LAND R. B., ^{SALES D.} T., 1977 . Mating behaviour and testis growth of Finnish Landrace, Tas-

manian Merino and crossbred rams. Anim. Prod., 24, 8 3 - 90 .

L EE

W. K., C UMMING I. A., ^{de K RETSER D.} M., ^{F INDLAY} J. K., H UD SON B., KEO G H E. J., 197 6.

Regulation ^of gonadotrophin secretion in rams from birth to sexual maturity. ^{I Plasma} LH, FSH and testosterone levels. J. Reprod. Fert., 46, ^{1 -6.}

L

EGAULT C., ^{G RUAND} J., ^{O ULION} F., 1979 . Mise au point et intérêt génétique d’une méthode

d’appréciation ^sur le vivant du poids des testicules chez le jeune ^verrat. Jouvnees ^{Rech. Por-}

cine en France, 313-322.

P

ELLETIER J., ^{K A NN} G., ^{D OLAIS} J., ^{ROSSEL I N G., 19 68.} Dosage radioimmunologique ^{de 1’hor-}

mone lutéinisante plasmatique chez le Mouton. Mise au point ^{de la} technique ^de dosage. ^{C. R.}

Acad. Sci., Paris, ^Ser. D, 266, 229I-zz94!

PROUD D., ^{D ONOVAN} D., ^{K I NSEY} R., ^{CUNN I NGHAM P.} J., ^{Z I MMERMAN D.} R., I9’!6. ^Testicular growth ^{in boars as} influenced by selection. J. ^Anim. Sci., 42, 13 6 1 -6 2 (Abstr.).

T HIM O

NIER J., ^{MA ULEON} P., 19 6 9 . Variations saisonni6res du comportement d’oestrus et des activites ovarienne et hypophysaire ^chez les ovins. Ann. Biol. Anim. Bioch. Biophys., 9, 233 - 250.

T HIM ON I

ER J., ^{PE LLETIER} J., ^{LAND R.} B., I 972 . The concentration of plasma ^LH in male and female lambs of high ^{and low} prolificacy ^breed types. J. Reprod. ^{Fert., 31,} 49 8- 499 .

T ROUNS O N

A. 0., CHAMLEY W. A., ^{K ENNEDY} J. ^{P., TASSEL R.,} 197 4 . Primordial follicle num-

bers in ovaries and level of LH and FSH in pituitaries ^and plasma ^{of lambs selected for and} against multiple births. Aust. J. ^Biol. Sci., 27, 293 - 299 .

WESTHUYSEN J. M., ^{D IERK SE} E., 1977 . The use of plasma luteinizing ^{hormone as an indicator}

of prolificacy ⁱⁿ sheep. ^{S. Afv.} J. ^{Anim. Sci., 7, 157 - 159 .}